Tows of synthetic filaments and method for making the same



Get. 29, 1968 5. DAVIES ETAL TOWS OF SYNTHETIC FILAMEN'SS AND METHOD FORMAKING THE SAME Filed Jan. 11, 1965 I Y g/\\ L I 1 l I O O O O O O O(Move? United States Patent ABSTRACT OF THE DISCLOSURE- A tow and a'method for'producing said tow which is suitable for stretch-breakingproduced by extruding a polyamide having a relative viscosity of lessthan about 30 into a plurality of filaments whichmake up the tow. Thetow is split into a plurality of bundles or sub-tows and each bundle isthen subjected to a different tensioning prior to drawing. The bundlesare then reformed into the tow and draw-crimped. The resulting tow hasan improved snap-break rating and a more desirable load extension curve.

This invention relates to improvements in or relating to tow and to amethod of producing the same, the said tow consisting of filaments of apolyamide, and is particularly concerned with tow which is intended tobe converted into slivers and spun into Schappe-type yarns.

Tows, such as 100,000 denier 1 /2 denier per filament 66 nylon tow,intended for the production of Schappetype yarns are converted intoslivers on a stretch-break- :ing machine and the slivers then processedinto the spun yarn. A typical stretch-breaking machine is the Seydel- Vstretch-breaking machine the essential parts of which are brieflydescribed below.

The Seydel stretch-breaking machine consists essentially of twosections, a stretching section and a breaking section. Nearly all of thestretching is done in the stretching section between the various headsof the machine of which there are normally six. Each of these. headsconsists of a series of rollers in a 3 over 4 arrangement in which thereare four positively driven steel rollers with three plastic-coveredjockey rollers in the intermediate gaps. The tow is laced through theserollers such that it passes under each of the four steel rollers andover each of the three jockey rollers in succession. The surface speedof the driven rollers in any one head is the same, but the surface speedof the rollers in the different heads increases from the feed (creel) tothe delivery end of the machine.

The breaking section consists of two pairs of rollers; the

near pair, referred to as the intermediate rollers, is at the same timethe seventh head of the stretching section since it has a higher surfacespeed than that of the rollers of the sixth head. The intermediaterollers consist of a positively driven steel roller and a rubber-coveredpressure roller, and the front pair of rollers a positively driven steelbottom roller and a leather or rubber-covered top pressing roller. Inorder that these rollers should be enabled to grip the tow sufiicientlytightly to avoid slippage when breaking, the pressure exerted by therollers is about 400 lb. and 2,500 lb. respectively.

The path of a single tow through the machine is called a channel and themachine may be designed to enable it to take four channelssimultaneously.

One of the difiiculties encountered in the use of this type of machineis that of so called snap breaking which occurs particularly whenrestarting the machine following a voluntary or involuntary stoppage,although 3,408,251 Patented Oct. 29, 1968 ice 2 it may also occur duringapparently normal running. The snap-break occurs in the stretchingsection of the machine and results in all of the filaments in onechannel of the tow breaking so that the restringing of that tow isnecessary. Since the restringing requires that the machine be stopped,there is the possibility that a snap-break will occur in one of theother channels of two-on restart.

It is believed that major factors in the occurrence of snap-breaks in atow are interfilament adhesion and filament damage caused by the nipofthe rollers in the stretching section of the stretch-breaking machine.

Interfilament adhesion increases (a) along the length of the tow in thestretching section and'(b) when the tow is stationary in the machinee.g. during a stoppage. The physical factors involved are the tension inthe tow due to stretching, the'normal pressure of the rollers againstthe tow and the pressure at the nips between the rollers in each head.The increasing tension in the t-owas it travels through the stretchingsection produces increasing normal and nip pressure as it passes aroundthe rolls. These tensions and pressures are sufficiently great to deformthe filaments from circular to hexagonal crosssection and sometimes tocause fusion. These hexagonal filaments will give an increased surfacearea of interfilament contact and therefore increase the risk ofadhesion. Filament adhesion binds the tow either partially or completelyinto a solid ribbon.

Damage to the filaments between the roller nips introduces a line ofweakness across the tow. If one or more of the filaments across thisline break soon after restart the relatively unchanged total stressacting on the remaining filaments in the ribbon is excessive and causesmore filament breakage. Breakdown of the tow is then rapid and asnap-break frequently occurs.

Filament adhesion is thought to be the most important factor since asnap-break would be initiated by the weaker filaments in the solidribbon irrespective of the method of weakening these filaments.

It is a necessary feature in the processing of 100,000 denier nylon towson the stretch-breaking machine as described above, that a largeproportion of filaments are broken in the stretching section in order toreduce the strength of the tow sufficiently to prevent slippage at thefront pair of rollers in the breaking section. In a tow having highfilament adhesion this deliberate breaking action helps to promotesnap-breaking at restart and may also be at least partly responsible forthese snap-breaks which occasionally occur during normal running.

We have now found that in order to have a good snapbreak rating, i.e. aminimal tendency to snap breaking, a tow should have a low breaking loadand a wide spread of physical properties, particularly filamentextensibility. The low breaking load enables lower tensions being usedin the stretching section of the stretch'breaking machine and thus leadsto less interfilament adhesion and nip damage, since the lower thetension the lower the pressure at the nip between the rollers. Also alower tension in the tow means that a smaller percentage of filamentsneed to be broken in the stretching section to prevent slippage at thefront rolls in the breaking section of the stretch-breaking machine. Awide range of filaments extensibilities enables the less extensiblefilaments to be broken in the stretching section and the strength of thetow reduced before the breaking point for the other filaments has beenreached.

The snap-break rating of a tow on a Seydel stretchbreaking machine isdetermined in the following manner. The overall draft of the stretchingsection is adjusted so that no tow slippage occurs between the rollersof the breaking section. Four tow channels are used and ten restartsmade after voluntary machine stoppages of f: 1; '73 -5'minutes durationgiving ery speed of the tow is set; at 96 ft./min. at a breaking sectiondraft of 1.8 and the tests carried out at an ambient temperature of. 78F. anda relative humidity of 60%. ;.The snap-breakrating is thencalculated from the expres- .sion i {Percent rating; a

[Number ofsnap=breaks -+tN.umber of veryzthin v places X3)+(Number.ofthin places X1) a -,'.4OX'1O-- s :v

10,..ar1d

40 tests per .sample...'lhe.deli v.-...

preferably less th,anl .;i f thetowto be capable ofjbeing Although a towhavinga limited spread of physical properties, such as extensibility,can be produced by varying the spinning conditions, 'a wider and moresignificant "spread can be obtained at the draw crimping stage in theproduction of tow by using various yarn paths in the I squirrel cage'ofthe draw crimper.

were subjected to the same tension'in thesquirrel cage of For thepurpose of this description a .squirrel cage may be described as anarray of bright chrome bars arranged so that the tow can be interlacedthrough the bars to insert tension in the tow.

Thus by increasing the angle of Wrap around the guide bars in thesquirrel cage for some of the filaments in the ,tow and thereforeincreasing the tension in these filaments relatively to the remainder,the more highly tensioned filamentsare stretched or drawn to some extentin the .squirrel cage. Because of the stretching of some 'of thefilaments in the tow the draw-crimper draw ratiohas to .be reduced toprevent breakage of the filaments either in the squirrel cage or in thedrawing zone of the drawcrimper. The resulting crimped tow containsfilaments .,drawn to difierent degrees and hence having a range offilament extensibilities.

Aa tow having a suitably 10w breaking load, preferably less than 500kg./ 100,000 denier, can be obtained by's'pin- .ning the"filamentsconstituting the tow from asynthetic 'high molecular weightpolymer, e.g. polyhexamethylene liadipamide, having a relative viscosity(R,.V.) of 30 or less and preferably in the range 27-30. w

' Relative viscosity of a polyamide is defined as being the ratio of theviscosityof a solution thereof in ninety percent by weight formic acidcontaining 11 grams'of polyamide per 100 ml. of solution at C., to theviscosity of ninety'percent'formic acid at the same temperature. I

The increase in the range of filament extensibility required in a towfor it to have a good snap break rating can be'defined by reference tothe load extension curve of the tow. A typical load extension curve fora normal tow consisting of polyhexamethylene adipamide filaments 'isshown in the drawing curve A in which L is the breakingload in kg., i.e.the maximum load achieved during extension, and S is the length of thetail of the load-extension curve. The tail S is defined as being theextension in centimeters required to reduce the load from 200 to 25 kg.In order to have an improved snap-break performance the length of thetail should be at least l cm. greater than that of an equivalent tow inwhich all of the bundles of filaments were subjected to the same tensionin the squir- -rel cage. The effect on the load extension curve of'forrn- -ing a tow from filaments spun from polymer having an R:V.:'ofless than 30 and whichhave been subjected to 'different'tensions in thesquirrel'cageis shown by curve B 0f thedrawing- The value of thebreaking load, L ,'is lower-and the length of the tail S considerablyincreased.

thereisip q id s. .suitable for, .stretcl tebreaking ,wherein the.filarn The load extension. curve .is determineiusiuguan. Instron tensiletester (registered trade mark) fitted with special clamps which aredescribed in British patent application No. 937,818. In the test 20 cm.unsupported length of sample is extendedatSO-ctriL/min. Q

j aspect ffthi s ihventio Wherefore, LMQ

ingthe tow are xtrudedfrom apolya'rnidehaying'a relative viscosity of30.0}; less andare subjected toatleasttwo different levels of tension inthe squirrel icage of a drawcr'iniping *riiachine and are then 1drawnand-crimped according to known proc edures. 7

According to'anoth' r aspect ofthis' invention there is provided a towconsistingofpolyamide filaments produced by the above-mentioned processhaving a snap break-rating'(as hereinbefor'e defined)..'of less than 10and having a load extension curve in the tail (ashereinbefore defined)isjat least 1 .cm. longer than the tail of the load extension curve of atow in which. all the filaments the draw crimping machine.

,Theimproved stretch-breaking performance of tows -p roduced according,to this invention will now. be illustrated by the following examples,which examples are V invno way intended to limit the scope of theinvention.

Example 1 1 v A 100,000 denier. tow comprising 11 bundles of fila mentsof polyhexamethylene adipamide (each filament being of 1 /2 denier)spun-from polymer having a relative viscosity (R.V.) of 27 is passedinto the squirrel cage of a conventional draw-crimpingmachine. Fivebundles of filaments are passed around the guide bars at a sufficientlyhigh'angle of wrap to'cause drawing to occur at this stage,

the remaining 6 bundles of filaments are passed through at the normaltension. After passing through the squirrel cage the bundles offilaments are recombined and'drawcrimped using a draw ratioof 2.64 inthe usual manner. The resultant tow had a snap-break rating of 3 whenprocessed on a Seydel stretch breaking machine. The load ex tensioncurve for the tow had a tail Set 3.4 ems-An identical tow processed inthe same way except that all the bundles of filaments were subjected tothe same tension in the squirrel cage and the tow drawn using a drawratio of 3.0,ha'd a snap-break rating of- 98 and theloadextens'ionIcurve had a tail S of 1.5 cm., i.e. 1.9 cm. shorterthan-the tow processed according to the invention.

Example 2 Two tows identical to those employed in Example -1 weresimilarly processed but were steam-set for 7 minutes at 25 'p.s.i. 'in aSanderson steam setting cabinet before testing on the 'Instron tensiletester. The normal tow had a snap-break rating of 87 and a loadextension curve having a tail 8 of 1.4 cm s. whereas the tow containingfilaments subjected to diiferent levels of tension had a snap-breakrating of 4 and atailS to the load extension curve of 2.7 cm.', i.e. 1.3cms; longer.

What we claim is: j 1. A process forthe production of a tow suitable for"stretch breaking comprising forming a tow of filaments by extrudingsaid filaments from a polyamide having a relative VISCOSitY of not morethan 30, forwarding said tow to the squirrel cage of a draw-crimpingmachine, subjecting at-least one portion of the filaments forming thetow toa different level of tension in said squirrel cage compared tothe'remainder of the filaments of said tow and then'drawing and crimpingsaid tow thereby'producsaid bundles to different levels of tension priorto drawing and drawing, crimping and recombining said bundles into a towthereby producing a tow of improved stretch breaking characteristics.

3. A process according to claim 2 wherein the polyamide has a relativeviscosity in the range of 27-30.

4. A process according to claim 3 wherein the polyamide ispolyhexarnethylene adipamide.

5. A tow comprising a plurality of crimped polyamide continuousfilaments wherein said filaments have a breaking load of less than about500 kg./ 100,000 denier and wherein a proportion of said filaments insaid tow has a difierent draw ratio compared to another proportion offilaments in said tow, said tow having a snap-break-rating of less than10.

References Cited UNITED STATES PATENTS 2,385,890 10/ 1945 Spanagel.3,011,215 12/1961 Alley. 3,114,999 12/ 1965 Coggeshall.

ROBERT F. BURNETT, Primary Examiner.

L. M. CARLIN, Assistant Examiner.

